Larger pipe products are produced under a variety of industrial trade standards or regulations, as well as end user design specifications. As a consequence, a considerable amount of data concerning manufacturing history and the like are associated with each production run of such products.
As part of an industry effort to maintain quality standards, as well as to assure proper usage in the field, typically, identifying data are applied to each length of pipe or tube at the time of production. Because the outside surfaces of pipe products often are coated or wrapped, those surfaces often are not available for such marking. Accordingly, it has been found necessary to position such data on the circular inside surfaces of pipe product near one open end. Typically the marking procedure has been carried out manually by personnel utilizing a hand-held paint sprayer in conjunction with a flexible stencil which is positioned over the inside surface. As the amount of marking data has increased, this manual procedure has been found to be cumbersome, time consuming, and prone to human error.
Investigators have considered automated approaches to carrying out such marking, for example utilizing industrial spray marking systems, a marking technology which involves the formation of characters or symbols in dot matrix fashion using discrete dot-like deposits of marker fluid such as marker ink. Conventionally, this marker ink is expressed from select ones of a linear array of nozzles in conjunction with nebulizing air to form dots at the surface to be marked. When these linearly arrayed nozzles are called upon to mark a circularly shaped surface internally within a pipe structure, however, their marking performance has been considered unsatisfactory for a variety of reasons. In this regard, where the nozzle arrays are used according to conventional practice, i.e. moved with respect to the longitudinal axis of the pipe being marked, variations from nozzle-to-nozzle in nozzle-to-marked surface distance results in the formation of unsatisfactory characters. Fabricating the nozzle assembly as a circular array is impractical, inasmuch as the systems are called upon to mark pipe of somewhat widely varying diameters. Additionally, the mechanisms necessarily become unacceptably complex due to radial and axial alignment requirements for the nozzle support mechanisms.
Resort to the use of assemblies carrying character dedicated singular spray marker nozzles which are maneuvered in parallel with the axis of the pipe being marked has been considered. With such approach, one or more character dedicated nozzles are moved by a traversing mechanism along an undulating locus generally parallel with the axis of the pipe being marked. Where fifteen characters formed within a conventional 5.times.7 dot matrix format are involved for each nozzle, about 90 short, quick moves are required of the traversing mechanism. Thus, where such mechanisms are called upon to mark or create a practical number of characters, the number reciprocal mechanical motions required of the support and drive mechanisms becomes excessive with a resultant unacceptable time-of-marking expenditure. Similarly, where single nozzles are dedicated to form one row of characters oriented transversely to the pipe axis, a very high accuracy is required of the traversing/timing system, in that dot or pixel-to-pixel accuracy must be better than one pixel element (e.g. 0.2 inch) after forming five to seven paths within the pipe. As before, such an approach is slow, inasmuch as one nozzle must form a complete string of characters.
From the foregoing, it may be observed that a marking technique is called for which accommodates a marker unit to the curved surface of the pipe to be marked while remaining capable of providing a plurality of lines of data within the generally limited window of available marking time experienced, for example, in a pipe production facility. This expedited marking procedure further should be carried out without the involvement of complex translational movement defining machinery and associated controls endemic to the procedures and equipment proposed in the past. A comparatively simple, efficient system having enhanced printing speeds is desired for such in-plant marking systems which, additionally, may be integrated into the pipe treatment aspects of production. The latter aspects include, inter alia, automated pipe length measuring stations, weighing stations, and the like.